You have many times made it clear that proper tire pressure is very important. My question is - how much over inflated or under inflated is OK to go ahead and drive without having to either let air out for overinflation or get out the old air compressor and add air to the proper amount?
First requirement is measure it in the morning when the tires are cold. That’s the only time to reduce pressure if needed (2 psi high is fine with me). More than 2 psi low I’d definitely add. Adding to a low tire applies whenever you measure it, but check it again when they’re cold.
A car can tolerate a lot more over inflation than under inflation (because a tire is more likely to fail if it is underinflated).
I am of the opinion that 3 psi low and up to 5 psi over are acceptable limits. How to get that?
Set the pressure at a moderate temperature with a few psi more. For example if you set the pressure on a summer’s morning, it probably won’t be too high in the heat of the afternoon.
Rule of thumb: Passenger car tire pressures follow the outside temperature at the rate of 1 psi for every 10°F. So setting a pressure at 70°F would rise 2 degrees when it reaches 90°F.
This is particularly useful for setting pressure in the winter, where the garage is - say - in the 50’s and the outside is in the 20’s. You’ll want to set the pressure 3 psi high in the garage so that it is optimal at the outside temperature.
And if you are anticipating a -20°F, you’ll want to adjust for that as well - keeping in mind that it is better to be over inflated rather than under inflated.
Please note that it is NOT a good idea to set your pressures when the outside temp is 35°F or below as the water in the air can freeze on the tire valve and cause it to leak.
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Thanks - very good information. Appreciated!